1. Field of the Invention
The present invention provides for monitoring the continuity and integrity of communication trunks and more particularly for automatically monitoring communication trunks of a communication system.
2. Description of the Related Art
Communication systems comprise various communication equipment connected to each other by media (e.g., copper wire, coaxial cables, optical fibers) through which communication signals carrying information are conveyed. Communication equipment are various equipment that transmit and receive communication signals conveyed throughout a communication system. Communication systems are designed with media that have relatively large information capacities for conveying information within a communication system or between different communication systems. Such media are an important part of the infrastructure of communication systems and will hereinafter be referred to as communication links. Communication links are used, for example, to connect telephony systems to wireless communication systems. Communication links are logically configured as a bundle of communication channels commonly referred to as communication trunks.
Referring to FIG. 1, there is shown a wireless communication system (100) that uses communication links for interconnecting its communication equipment and to also connect to another communication system. The other communication system is a well known telephony system known as the Public Switched Telephone Network 142 (PSTN) familiar to users of telephony equipment (e.g., telephones, facsimile machines). Wireless communication system 100 comprises Base Stations (BS) representing equipment that are part of or form cells. The cells are symbolic representations of distinct geographical areas that define the physical boundaries within which a base station conveys (i.e., transmits and receives) user information. In particular BS 128 forms cell 134, BS 130 is part of cell 136, BS 132 is part of cell 140, BS 133 is part of cell 138. The Base Stations are communication equipment including radios that convey communication signals (i.e., transmit and receive) between users within the cells and also convey information over communication trunks connected to Switch 118 and Processor 124. User information, commonly referred to as subscriber traffic, is information generated by users. The Base Stations also convey system information which is information generated by communication equipment to control and operate the communication system. An example of system information is signaling information used by communication equipment to regulate the flow of user information within a communication trunk. In portions of the current PSTN and in wireless communication systems such as communication system 100, the subscriber voice traffic is represented in digital form known as Pulse Coded Modulation (PCM).
Switch 118 and Processor 124 are part of the communication equipment that convey system information for operating and controlling wireless communication 100. Switch 118 and Processor 124 are typically co-located with other equipment at a location referred to as a Mobile Switching Center (MSC). Thus, both Switch 118 and Processor 124 are located at MSC 144. BS 130 is connected to Switch 118 via communication link 106. Communication trunk link connects BS 132 to Switch 118. Communication link 110 connects BS 133 to Switch 118. Each Base Station is connected to Processor 124 via a system communication link. For purposes of clarity, each system communication link is denoted by a broken line. The system communication links (104, 112, 108, 116) can be part of a communication link or they can be physically separate links. The system communication links are connected between the Base Station equipment and Processor 124. Processor 124 is also connected to Switch 118 via a system communication link (122). Only system information are conveyed through the system communication links. Under the control of Processor 124, Switch 118 routes user information between PSTN 142 and wireless communication system 100 with the use of communication trunks within communication link 120. Switch 118 also routes user system information through the various communication trunks of the communication links connected to the Base Stations of wireless communication system 100. In particular, communication links 102, 106, 110, 112 and 114 all comprise communication trunks which are used by communication equipment within communication system 100 to convey user information. One particular well known Switch is the 5ESS Digital Cellular Switch (DCS) designed and manufactured by Lucent Technologies of Murray Hill, N.J. The system information is generated by Processor 124 allowing Processor 124 to control Switch 118 and control the operation of the communication trunks. System information is conveyed between Processor 124 and Switch 118 over system communication link 122. Processor 124 sends commands to Switch 118 over communication trunks within communication link 122 instructing Switch 118 to perform various system operations for the control the operation of the communication trunks.
BS station 128 is connected to Switch 118 via communication link 102. The physical length of some communication links is such that sometimes the communication signals suffer some degradation. In such cases, the communication links are provided with relay communication equipment (e.g., Relay 126) that revitalize the communication signals propagating through such communication links. Signal degradation also occur because of physical deformities (e.g., damaged cable) present at one or more points along the communication link.
The successful operation of wireless communication systems and other types of communication systems is largely dependent on the communication trunks used in such systems. System operators, i.e., owners of communication equipment and communication trunks, have used standard techniques for monitoring communication trunks and for determining whether such trunks are operating properly. For ease of understanding and for the purpose of illustration, a typical technique for monitoring a trunk is discussed using a communication trunk within communication link 102.
A craftsperson, typically employed by the system operator, first determines whether a trunk within link 102 is idle. An idle trunk is a communication trunk through which no user information is being conveyed. The craftsperson determines whether a particular trunk is idle by obtaining such information from Switch 118 or Processor 124. Such information is processed and stored in accordance with the protocol being followed by communication system 100. A protocol is a set of rules that define how communications between users and between communication equipment are initiated, maintained and terminated. It should be noted that a craftsperson can request that a trunk be made idle in which case Switch 118 under the control of Processor 124 removes subscriber traffic from the trunk to make the trunk idle.
Once a craftsperson has determined that trunk 102 is idle, the craftsperson sends a command (or commands) to Processor 124 requesting that the trunk within link 102 be taken out of service and then tested. Service to the users of the trunk is thus interrupted. The craftsperson sends the command by operating Processor 124 causing said equipment to transmit information recognized by Switch 118 as a request to take the trunk out of service and then to perform a continuity test for the trunk. Processor 124 also sends a request to BS 128 indicating that a particular trunk within link 102 is to be taken out of service and then tested. BS 128 typically comprises a test card (not shown) that is activated upon receipt of such a command and along with Switch 118 and Processor 124 performs the continuity test. BS 128 (and the other Base Stations) also comprises a radio (not shown) that transmits and receives communication signals over its corresponding communication link. Processor 124 seizes the trunk (within link 102) by taking complete control of the operation of the trunk. Processor 124 then takes the trunk xe2x80x9cout of servicexe2x80x9d (OOS) meaning that no user information is henceforth allowed to be conveyed over the seized trunk until the trunk has been tested and released or put back into service. Processor 124 sends commands over system communication link 122 to instruct Switch 118 to operate the OOS trunk within communication link 102 in a test mode. Processor 124 also instructs (via system link 104) the test card in BS 128 to operate in a test mode. Test mode operation involves the transmission of certain audio tones through the OOS communication trunk being tested from Switch 118 to the test card of the corresponding Base Station (i.e., BS 128). In response, the test card in the corresponding Base Station transmits the same tones or different tones back to Switch 118. Switch 118 is programmed or set to detect the same tones or different tones. The communication trunk (within link 102) is operating properly if Switch 118 receives the proper tones transmitted by the test card at BS 128 within a defined period of time. Otherwise, the communication trunk is deemed to be non-operational. Thus, the test determines whether communication signals transmitted over the communication trunk are received by BS 128, i.e., the continuity of communication trunk is tested.
Performing a continuity test on a communication trunk in the manner described above has several drawbacks. First, the continuity test determines the current status of a trunk; it does not monitor the trunk continuously to determine if the status has changed. It is certainly possible, and reasonably likely, that a trunk that has been tested and deemed to be operating properly can become non-operational at any time after the continuity test has been completed.
Second, the continuity test requires that the trunk be taken out of service. An out of service trunk is unavailable to users for the period of time during which the continuity test is being conducted and thus the efficient use of such a trunk is adversely affected. Third, the continuity test has to be initiated by a craftsperson. The use of a craftsperson to initiate such a test is an added maintenance cost to a system operator.
Fourth, the continuity test simply determines whether there are any breaks in the communication link that would prevent a signal (i.e., a tone or tones) from being received by a base station located at one end of the communication link. Many communication links, such as link 102, have one or more intermediate equipment (e.g., relay equipment 126) connected thereto that, if improperly administered, can reflect the transmitted tone or tones back to Switch 118. If Switch 118 is set to receive the same tones that it transmitted, communication trunk link may be falsely deemed to be operational when in fact section 102a of communication link 102 has not been tested and may have a break in continuity.
The continuity test does not test the integrity of the communication links or the trunks within said links. The integrity of a communication link (or trunks within said link) is its ability to provide information that is intelligible at either of its ends. Thus, for a link of acceptable integrity, the equipment at either end of the communication link are able to receive intelligible information. The communication link may be in relatively poor physical condition or may have relatively poor electrical and/or optical characteristics that adversely affect the quality of the communication signals that propagate through it. Some well known manifestations of poor characteristics are signal amplitude degradation, phase jitter and frequency translation. In spite of these poor characteristics, a communication link may still be deemed operational from the results of a continuity test.
What is therefore needed is a method for monitoring automatically a communication trunk within a communication link to determine its integrity without having to take the trunk out of service and without the need of a craftsperson to initiate the testing of such a trunk.
The present invention provides a method for automatically monitoring communication trunks of a communication system on a periodic or aperiodic basis without using a craftsperson and without interrupting service to users of the communication trunk. First, the method of the present invention selects a trunk for testing. If it is determined that the selected trunk is idle, the trunk is tested. Otherwise the method of the present invention selects another trunk in accordance with a trunk selection algorithm. The selected trunk is tested for continuity and integrity by transmitting a particular test message over the trunk and receiving within a defined period of time a responding test message. The test will be interrupted at any time a need for its service to users arises. When a trunk has failed the test, it is taken out of service and the service provider is advised of the failure. After a trunk has passed the test or failed the test or a test has been interrupted, the method of the present invention selects the next trunk to be tested in accordance with trunk selection algorithm.